A wide variety of semiconductor packages having integrated circuits mounted to printed circuit boards are now used in many products. Technological advances in integrated circuit (IC) materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. Concurrent with the change in size and complexity, has been an increase in the number of connections from the integrated circuit to the larger electronics assembly, including the printed circuit board.
One of the current packaging processes for ICs employs “flip chip” technology, where an IC is flipped and bonded to a carrier substrate, such as a printed circuit board (PCB). Often, the input and output connections between an IC and carrier substrate are created using a ball grid array (BGA). The input and output connections conduct electrical signals from the integrated circuit to the printed circuit board in which or on which the IC package is associated.
BGA packaging offers advantages, such as improved heat conduction due to the lower thermal resistance between the package and PCB, a lower inductance connection than pins, and reduced solder connection bridging. As a result, BGA packaging has become a favorite packaging type for many manufactures. Typically, during assembly of a ball grid array (BGA), an IC package and printed circuit board (PCB) are heated, causing solder balls to melt and solder the IC package to the PCB.
In general, the solder connections between a BGA and a PCB require tight mechanical tolerances during processing in order to preclude mechanical stresses which would promote solder joint failure. However, temperature fluctuations and the design of a given PCB may result in excessive thermal stress, which may then lead to warpage of the PCB. To counter the possibility of warpage, most PCBs are designed symmetrically, but this imposes many design limitations. Typically, if a PCB is found to have undesirable degrees of warpage, then the PCB can not be used. As a result, PCB warpage can quickly increase costs of production since PCBs are usually produced in batches.